JPS59115725A - Concentrating method of oxygen - Google Patents

Abstract

PURPOSE:To recover the oxygen adsorbed in an adsorption column and to improve the recovery rate for gaseous oxygen in a method for producing oxygen by a pressure swing adsorption method by washing the adsorption column, upon ending of an adsorption stage, with gaseous nitrogen. CONSTITUTION:An adsorption column is changed over by a selector valve to stages for pressure adsorption, vacuum regeneration and repressurization so that the gaseous nitrogen in raw material air is adsorbed and gaseous oxygen is continuously produced. The adsorption column upon ending of the pressure adsorption stage of a method for producing oxygen by a pressure swing adsorption method is washed with gaseous nitrogen, and slightly concd. gaseous oxygen is obtd. The gas contg. the concd. oxygen is reutilized as a gaseous raw material. The recovery rate for the gaseous oxygen of the product is thus improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating and producing oxygen gas from air by pressure swing adsorption.

There is a pressure swing adsorption method (hereinafter abbreviated as PSA method) as an oxygen production method for producing oxygen using air with an original value of <1. The method shown in FIG. 7 is an example of a conventionally known method, in which raw air is sent through a pipe 1 to a compressor 2, where it is pressurized to approximately j] (q/cr/l). , tube 3
Then, it is sent to seven adsorption towers 7 out of the three adsorption towers 7, 8.9 which are used selectively by the switching valves 4a, 5a and aa. Each adsorption tower 7, 8,
The column 9 is filled with an adsorbent such as zeolite that selectively adsorbs nitrogen, and the nitrogen in the air introduced under pressure is adsorbed, and the outlet of the adsorption column 7 is filled with an adsorbent that selectively adsorbs nitrogen. Product oxygen gas is obtained. This product oxygen gas has a switching valve 10
It is sent to the supply destination via the b1 pipe 13 and the flow control valve 14. "Pressurized adsorption step" On the other hand, the adsorption tower 8tj, which has been saturated by adsorbing nitrogen as described above and is in the regeneration step: After being depressurized, a part of the product oxygen gas is branched through the pipe 15, and the pressure is adjusted. By valve 16/k
Gas (purge gas) under pressure of about r/C11 is
It flows back through the column 8 via the pipe 17 and the switching valve 11a. This purge gas desorbs nitrogen from the adsorbent and becomes waste gas containing nitrogen gas, which is released into the atmosphere through the switching valve 5b and the pipe 18. "Low-pressure regeneration process" In addition, after being purged from the 9-layer low-pressure regeneration process in the adsorption tower, a part of the product oxygen gas is further introduced, and approximately j kq
/cr! It is kept in a state where it is repressurized to a certain degree and is waiting for the next adsorption step. "Repressurization step" As described above, the oxygen production method using the PSA method is performed by sequentially switching the three adsorption towers 7.8.9 to the pressure adsorption, low pressure regeneration, and repressurization steps. , so that a continuous flow of oxygen gas is obtained.

By the way, in this oxygen production method using the PSA method, a rich product oxygen gas is required to regenerate the adsorbent, and in order to enter this "low-pressure regeneration process", the pressure in the adsorption tower must be depressurized. However, at this time, the oxygen content adsorbed in the adsorption tower is discharged to the outside, which has the drawbacks of poor yield of product oxygen gas and high power costs. The following points can be cited as the main means of solving this problem.

(a) Make it possible to desorb nitrogen without using product oxygen gas.

(Towards) Vacuum regeneration is a conventional improvement method that has been used from the viewpoint of (a) above to reduce as much as possible the amount of oxygen gas that is adsorbed by the adsorbent and discarded. In this method, the tower that has completed the adsorption step is emptied of Tc, and the adsorbed gas (nitrogen) is desorbed and regenerated. Since no purge gas is used to regenerate the adsorbent, the product recovery rate is improved.

On the other hand, in the above ←), the oxygen present in the adsorption tower is exhausted to the outside due to pressure reduction (pressure release) during the transition from the "pressure adsorption process" to the "low pressure regeneration process", so the amount of oxygen that is exhausted is The aim is to reduce the As an improvement method that has been conventionally carried out from this point of view, there is a process as shown in FIG. As shown in the figure, this method employs a partial pressure equalization process and is designed to remove product oxygen gas without introducing feedstock air, so the pressure inside the column gradually decreases. Become. As a result, only a small amount of depressurization is required in order to proceed to the regeneration process, and the amount of oxygen gas disposed of to the outside can be reduced.

By the way, when looking at the product recovery rate as a result of the above improvements, it is found that when obtaining a product oxygen gas with a concentration of 7%, the vacuum regeneration method described above yields 60 to 70 g. ” Takebayashi “Separation Technology” Vol. 21 No. J (/1/) p//~], and the purge method described later can be used to condense atmospheric oxygen by using SA separation. , Morishita, ``Toyo Soda Research Report'' Vol. 26 No. 7 c) 2F, 2) p9 ~ yoυ]. However, the current situation is that power costs still account for a large proportion, and there is a need for further improvement in the recovery rate in order to reduce power costs.

In the present invention, Nagisa et al. have developed a method for recovering oxygen gas from air using the PSA method, and in order to improve the recovery rate of oxygen gas, there is a need for depressurization when transitioning from a pressurized adsorption process to a low-pressure regeneration process. As a result of various studies on ways to significantly reduce the amount of oxygen wasted, the following findings were obtained.

In other words, the concentration distribution inside the adsorption tower after the adsorption process is shown schematically as shown in Figure 3, where there is a relatively oxygen-enriched area (the so-called adsorption zone) in the upper part of the tower. However, the other parts are in equilibrium with air.

When a gas with a high concentration of nitrogen gas (@degree angle θ or higher) is flowed into such a tower, as shown in Figure 1 (a), the area with high concentration of oxygen gas at the top of the tower is pushed out as it is. and K. If nitrogen gas continues to flow, the concentration of 9 elemental gases in the incoming gas is higher than the nitrogen gas concentration in the tower (in equilibrium with air), so some of the adsorbed oxygen is desorbed, and as a result, some of the adsorbed oxygen is desorbed. As a result, as shown in Fig. 3('b), a portion where the oxygen gas is somewhat concentrated is formed and the pressure increases. Finally, all of the oxygen-enriched portion mentioned above is pushed out of the tower, and the adsorption tower contains an extremely large amount of nitrogen gas (on the contrary, it is not adsorbed), as shown in Fig. The amount of oxygen gas present is low.

The above phenomenon is, so to speak, "cleaning by nitrogen gas" of the adsorption tower, and if the oxygen gas washed away and expelled from the adsorption tower is recovered, the product recovery rate can be improved.

There are two possible ways to recover the oxygen gas that flows out during the above-mentioned "cleaning with nitrogen gas": (a) mixing it into the product oxygen gas as it is, or ('b) using it as part of the raw material air. However, to obtain high purity product oxygen gas,
Method (b) is preferred.

Also, the nitrogen gas used in this cleaning process can be the gas obtained by depressurizing the tower after the cleaning process, or if there is another way to obtain nitrogen gas cheaply, you can use that nitrogen gas. Can also be done.

This invention (d) was made based on the above-mentioned knowledge, and the above-mentioned "cleaning with nitrogen gas" is carried out after the pressurized adsorption step.
The oxygen production method by the PSA method is configured to include the steps and means, and pressure is applied to concentrate the recovered oxygen gas.

An embodiment of the present invention will be described below with reference to the drawings.

The method of this invention is carried out using an apparatus as shown in FIG. In this figure, parts common to those in FIG. 7 are given the same reference numerals to simplify the explanation. In this device, a vacuum pump 20 for discharging nitrogen gas is newly installed, and this vacuum pump 20 and each of the adsorption towers 7, 8.9 are connected by a branched pipe 21. , each adsorption tower 7
There are switching valves 22.23°24 near ゜8.9, respectively.
is interposed. Further, a circulation pipe 27 having a nitrogen compressor 25 and a nitrogen tank 26 is connected to the pipe 18 used for exhaust gas discharge. This circulation pipe 2
Switching valves 28 and 29 are interposed near the connection portion of 7 with the pipe 18.

Further, a safety valve 30 is installed between the nitrogen compressor 25 and the nitrogen tank 26, and when the gas pressure in the nitrogen tank 26 exceeds a predetermined pressure, outside air is released. . In addition, a pipe 31 is provided in the pipe 3 near the compressor 2.
One end of the pipe 31 is connected, and the other three branched ends of the pipe 31 are connected to the adsorption towers 7.8 and 9 via switching valves 32, 33 and 34, respectively. .

The method of the present invention can be easily carried out due to the pressure of the apparatus having the above structure, and the process will be explained and explained by focusing on the adsorption tower 7 of this apparatus.

First, somewhat concentrated oxygen gas flowing out from the adsorption tower 9 after the pressure adsorption process is washed with nitrogen gas is passed through the pipe 31, and is transferred to the adsorption tower 7 after the repressurization process via the switching valve 4a. There will be an influx. At this time, the oxygen gas is sent from the adsorption tower 7 to the supply destination through the pipe 13 via the switching valve 10b.

Subsequently, the air is compressed by the compressor 2, passes through the pipe 3, and flows into the adsorption tower 7 via the switching valve 4a. As a result, the product oxygen gas is sent to the supply destination via the switching valve 10b and through the pipe 1.3.

Next, the nitrogen gas stored in the nitrogen tank 26 is repressurized by the nitrogen compressor 25, passes through the circulation line 27 and the pipe 18, and flows into the adsorption tower 7 via the switching valve 4b. As a result, the somewhat concentrated oxygen gas from the adsorption tower 7 flows through the switching valve 32 and the pipe 31 into the adsorption tower 8 after repressurization.

In the above process, the adsorption tower 7 filled with nitrogen gas is depressurized through the pipe 18, and the nitrogen gas that flows out is stored in the nitrogen tank 26.

Next, the gas remaining in the adsorption tower 7 is evacuated by the vacuum pump 20 via the pipe 21. Finally, the product oxygen gas produced in the other adsorption tower is transferred to the adsorption tower via the switching valve 10a. 7 and is pressurized again to the adsorption pressure, and is placed in a standby state for the next adsorption step.

FIG. 6 summarizes the above steps for each adsorption tower. Each of these steps is performed by sequentially switching a plurality of switching valves provided in each adsorption tower.

In the above explanation, the nitrogen gas for cleaning is stored in the nitrogen tank 26 and reused after cleaning other adsorption towers, but there are other gas sources that can supply nitrogen gas at low cost. If available, it may be used, or this gas source and the method described by Nitrogen Tajik 26 may be used in combination.

As explained above, in the oxygen production method using the PSA method, the present invention cleans the adsorption tower after the adsorption step with nitrogen gas, thereby leaving the oxygen adsorbed in the adsorption tower in a somewhat concentrated state. Since it is a method of recovering and reusing it as a raw material gas, the recovery rate of product oxygen gas can be greatly increased, and as a result, power costs can be reduced.

In order to quantitatively confirm the effects of this invention, the following experiment was conducted. .

〔Example〕

Experiments were conducted using the method and apparatus (FIG. 3) described in the above examples under the following operating and experimental conditions.

"Operating Conditions" Adsorption pressure... / ata~ata Nitrogen cleaning pressure...Pressure higher than adsorption pressure by θ/-ask/d Nitrogen pressure release...Pressure release to atmospheric pressure and vacuum evacuation
・-r O, / j OTorr raw material gas feed speed・・
・j~J Ocm/sec ('l column basis) Nitrogen cleaning flow rate.../% 20 rm/see (empty column basis) Adsorbent...Synthetic zeolite with pore diameter of jA or more "Experimental conditions" Adsorption pressure ...3 ata Nitrogen cleaning pressure ...3. Koata nitrogen pressure release
.../ata Vacuum exhaust ...1OOTOrr adsorbent
...Ca-A type synthetic zeolite As a result, the following experimental results were obtained, confirming the effects of this invention.

"Experiment results" Processed air amount.../Jt/ky Cycle product oxygen gas amount...Near 1/kf
・Cycle product purity... T-product recovery rate... Nitrogen gas concentration for T-o-chi cleaning... TAR% Recovered oxygen gas concentration..., Section 20-30

[Brief explanation of the drawing]

Figure 7 is an explanatory diagram of the conventional oxygen production method using PSA adsorption method, Figure 1 is a process diagram showing an example of the conventional oxygen concentration method,
Figure 3 is a schematic diagram showing the gas concentration distribution in the adsorption tower after the adsorption process has been completed; Figures 1 and 2 are for explaining an embodiment of the present invention, Figure 5 is a block diagram of a device suitable for carrying out this invention, and Figure 5 is a process diagram.2... ... Compressor, 7.8.9 ... Adsorption tower, 4a, 4b, 5a, 5b, 6a, 6b, 10a. 10b, 11a, 11b, 12a, 12b, 22゜23
．． 24.28, 29, 32.33.34...Switching valve, 25...Nitrogen compressor, 26...
Nitrogen tank. Applicant Nippon Sanso Co., Ltd. Agent Patent Attorney Masatake Shiga Figure 1

Claims (1)

[Claims] Multiple adsorption towers that preferentially adsorb nitrogen gas in the feed air are switched to each step of pressurized adsorption, depressurized regeneration, and repressurization using switching valves, allowing product oxygen gas to be continuously produced. In the method for producing oxygen by pressure swing adsorption method f,
A nitrogen cleaning step is provided to obtain a somewhat concentrated oxygen gas by cleaning the adsorption tower that has completed the pressure adsorption step with nitrogen gas, and the somewhat concentrated oxygen gas obtained in this step is used as a raw material gas. An oxygen enrichment method characterized by reuse.